Emergent superconductivity in single-crystalline <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>MgTi</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math> films via structural engineering
Wei Hu, Zhongpei Feng, Ben‐Chao Gong, Ge He, Dong Li, Mingyang Qin, Yujun Shi, Qian Li, Qinghua Zhang, Jie Yuan, Beiyi Zhu, Kai Liu, Tao Xiang, Lin Gu, Fang Zhou, Xiaoli Dong, Zhongxian Zhao, Kui Jin
Abstract
Spinel compounds have exhibited rich functionalities but have rarely shown superconductivity. Here, we report the emergence of superconductivity in the spinel ${\mathrm{MgTi}}_{2}{\mathrm{O}}_{4}$, known to be an insulator with a complicated order. The superconductivity is achieved by engineering a superlattice of ${\mathrm{MgTi}}_{2}{\mathrm{O}}_{4}$ and ${\mathrm{SrTiO}}_{3}$. The onset transition temperature in the ${\mathrm{MgTi}}_{2}{\mathrm{O}}_{4}$ layer can be tuned from 0 to 5 K in such a geometry, concurrently with a stretched out-of-plane lattice (from 8.51 to 8.53 \AA{}) compared to the bulk material. Such a positive correlation suggests ample room for further enhancement. Intriguingly, the superlattice exhibits an isotropic upper critical field ${B}_{\mathrm{c}2}$ that breaks the Pauli limit, distinct from the highly anisotropic feature of interface superconductivity. The origin of superconductivity in the ${\mathrm{MgTi}}_{2}{\mathrm{O}}_{4}$ layer is understood in combination with the electron energy loss spectra and first-principles electronic structure calculations, which point to the birth of superconductivity by suppressing orbital ordering. Our discovery not only provides a platform to explore the interplay between superconductivity and other exotic states, but also opens another window to realize superconductivity in spinel compounds as well as other titanium oxides.